Crower six stroke
The Crower six-stroke engine is a concept under development by Bruce Crower.
Two extra strokes are added to the customary internal combustion engine four stroke
Otto cycle, which makes a six stroke engine. A third down-stroke is a "steam stroke" and a third up-stroke exhausts the expanded steam while venting heat from the engine.
The engine cold starts on the Otto cycle, coasting through the fifth and sixth strokes for a short period. After the combustion chamber temperature reaches approximately 400 degrees Fahrenheit (200 °C), a mechanical operation phases in the fifth and sixth strokes. Just before the fifth stroke, water is injected directly into the hot
combustion chambervia the engine's fuel injector pump, creating steam and another power stroke. The phase change from liquid to steam removes the excess heat of the combustion strokeforcing the piston down (a second power stroke). As a substantial portion of engine heat now leaves the cylinder in the form of steam, no cooling systemradiator is required. Energy that is dissipated in conventional arrangements by the radiation cooling system has been converted into additional power strokes.
In Crower's prototype, the water for the steam portion of the cycle is consumed at a rate approximately equal to that of the fuel, but in production models, the steam will be recaptured in a
condenserfor re-use. Heat will be available from the condenser to provide interior heating of the vehicle, much as a conventional heater core works in cars and trucks today.
Crower claims a 40% reduction in
fuel consumptionand reduced exhaust emissions per a given power range. [ [http://www.autoweek.com/apps/pbcs.dll/article?AID=/20060227/FREE/302270007/1023/THISWEEKSISSUE Inside Bruce Crower’s Six-Stroke Engine - AutoWeek Magazine ] ]
The principal advantage present in the six-stroke design is the engine's ability to extract work from heat that is otherwise lost through the cooling system of a conventional four-stroke engine. Since the steam strokes have the side-effect of cooling the engine internally , this will allow the use of much higher
compression ratios, allowing the full potential of a fuel to be extracted. Since heat that previously would have been drawn out of the engine via the cooling system can be harnessed, compression ratios once useable for only short term applications (such as race engines) could conceivably be used in regular, long-running time scenarios without environmentally harmful anti-knock chemicals. Ultra-lean air/fuel mixtures, desirable for low emissions and high efficiency, may be used since excess heat, undesirable in other engine architectures, can likewise be harnessed in six-stroke applications. Under these circumstances, far more energy from fuel could be converted to useful output.
The weight and power loss of most conventional cooling system parts, such as the fan, radiator, and coolant pump, can be eliminated. On a large diesel truck, these parts may weigh as much as a thousand pounds. Fact|date=August 2008 At least a portion of this advantage is lost if water is recovered from the exhaust through a condenser.
The mechanical modifications needed to "six-stroke" a small air-cooled industrial diesel already being manufactured are far less complicated than any hybrid system. Fact|date=August 2008 Many maintenance features of this engine would be parallel or identical to the knowledge base of mechanics well-versed with gasoline, diesel, and racing engines.
Physical engine size reduction (per a designated power rating) is possible as one third of the engine strokes produce power (in the Crower six-stroke), instead of one quarter (in the Otto cycle). This, and the extra power stroke being provided by using water instead of fuel, means there is a significant improvement to the fuel efficiency and pollution within a given power range, and this is in a field where small improvements create great interest.
The higher percentage of power strokes may allow lower working speeds, with higher
torqueoutput at lower and broader rpmranges. Lower working speed might allow designs with greater crankshaftdiameter, for engine dimensions with inherently more torque potential.
As a high pressure steam engine that does not need a certified
pressure boiler, the related hardware complexities, dangers, and weight penalties and certification requirements are removed.
Obstacles and problems
A warm-up period would be needed in all automotive applications. Power and efficiency is reduced during the warm-up period.
A steam-free cool down period is needed to clear water/steam from the engine.
Cold climate anti-freezing measures would be needed in the water reservoir.
Oil contamination, from the water/steam portion of the cycle, is an obstacle to be dealt with, though additional piston/cylinder sealing rings can be easily added and special oils used. Also, data from lubrication oil engineering systems for steam turbines is readily available to help identify likely concerns and possible "well-researched" remedies.
The weight of an
oil separatorand a water condenser are likely additions, although these will be far smaller and lighter than a conventional cooling system.
Endurance testing will likely identify components that may need to have upgraded materials designated, such as possibly using stainless steel for the valves, cylinders, and rings.
Prior artexist to Crower's invention, but no preexisting six-stroke patents were mentioned in his patent application. [http://www.google.com/patents?id=GMRnAAAAEBAJ&dq=1339176] [ [http://www.freshpatents.com/Method-and-apparatus-for-operating-an-internal-combustion-engine-dt20070201ptan20070022977.php?type=description Method and apparatus for operating an internal combustion engine invention ] ] As of May 2008, no patent has been awarded.
Possible engine configurations and applications
It should be noted that the Crower six-stroke is not the same technology as water injection, where water is added to the incoming air/fuel mixture to allow higher power output through internal cooling.
The "steam" power stroke and the "burning hydrocarbon" stroke may not produce the same amount of force as each other. A one-cylinder engine would run much smoother with a relatively heavy flywheel to smooth pulsations, much like the early large one-cylinder diesel industrial factory engines.
One down-stroke does not provide any power, and, as mentioned above, the other two down-strokes may each provide different levels of power. This suggests the most compact configuration that will provide an inherently smooth running operation is an in-line three-cylinder engine. Or|date=August 2008 Of course, many other configurations and cylinder quantities may work.
Although the Crower cycle could be made functional with a variety of fuels and RPM ranges, steam theory suggests it would be very useful when coupled with a
diesel cycle, which performs well in low-rpm long-stroke applications. Fact|date=August 2008
A Crower cycle engine may prove to be useful as a passenger vehicle power plant. If meeting automobile emissions standards proves troublesome, the design may prove useful in heavy engine applications such as transport diesel trucks, heavy equipment (bulldozers, etc.), buses, and stationary power generators.
Related US Patents
*1339176 Internal combustion engine May 4, 1920. Leonard H. Dyer invented the first 6-stroke internal combustion/water-injection engine in 1915.
*3964263 Six cycle combustion and fluid vaporization engine Jun 22, 1976
*4301655 Combination internal combustion and steam engine Nov 24, 1981
*4433548 Combination internal combustion and steam engine Feb 28, 1984
*4489558 Compound internal combustion engine and method for its use Dec 25, 1984
*4489560 Compound internal combustion engine and method for its use Dec 25, 1984
*4736715 Engine with a six-stroke cycle, variable compression ratio, and constant stroke Apr 12, 1988
*4917054 Six-stroke internal combustion engine Apr 17, 1990
*4924823 Six stroke internal combustion engine May 15, 1990
*6253745 Multiple stroke engine having fuel and vapor charges Jul 3, 2001
*6311651 Computer controlled six stroke internal combustion engine and its method of operation Nov 6, 2001
*6571749 Computer controlled six stroke cycle internal combustion engine and its method of operation Jun 3, 2003
*7021272 Computer controlled multi-stroke cycle power generating assembly and method of operation Apr 4, 2006
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